Search

The ubiquitous commensal Candida albicans, part of the human microbiota, is an opportunistic pathogen able to cause a wide range of diseases, from cutaneous mycoses to life-threatening infections in immunocompromised patients. Candida albicans adapts to different environments and survives long-time starvation. The ability to switch from yeast to hyphal morphology under specific environmental conditions is associated with its virulence. Using hydrogen nuclear magnetic resonance spectroscopy, we profiled the intracellular and extracellular metabolome of C. albicans kept in water, yeast extract–peptone–dextrose (YPD), and M199 media, at selected temperatures. Experiments were carried out in hypoxia to mimic a condition present in most colonized niches and fungal infection sites. Comparison of the intracellular metabolites measured in YPD and M199 at 37 °C highlighted differences in specific metabolic pathways: (i) alanine, aspartate, glutamate metabolism, (ii) arginine and proline metabolism, (iii) glycerolipid metabolism, attributable to the diverse composition of the media. Moreover, we hypothesized that the subtle differences in the M199 metabolome, observed at 30 °C and 37 °C, are suggestive of modifications propaedeutic to a subsequent transition from yeast to hyphal form. The analysis of the metabolites' profiles of C. albicans allows envisaging a molecular model to better describe its ability to sense and adapt to environmental conditions. [ABSTRACT FROM AUTHOR]

It has been previously demonstrated that synthetic antibody-derived peptides could exert a significant activity in vitro, ex vivo, and/or in vivo against microorganisms and viruses, as well as immunomodulatory effects through the activation of immune cells. Based on the sequence of previously described antibody-derived peptides with recognized antifungal activity, an in silico analysis was conducted to identify novel antifungal candidates. The present study analyzed the candidacidal and structural properties of in silico designed peptides (ISDPs) derived by amino acid substitutions of the parent peptide KKVTMTCSAS. ISDPs proved to be more active in vitro than the parent peptide and all proved to be therapeutic in Galleria mellonella candidal infection, without showing toxic effects on mammalian cells. ISDPs were studied by circular dichroism spectroscopy, demonstrating different structural organization. These results allowed to validate a consensus sequence for the parent peptide KKVTMTCSAS that may be useful in the development of novel antimicrobial molecules. [ABSTRACT FROM AUTHOR]

The previously described decapeptide AKVTMTCSAS (killer peptide, KP), derived from the variable region of a recombinant yeast killer toxin-like anti-idiotypic antibody, proved to exert a variety of antimicrobial, antiviral, and immunomodulatory activities. It also showed a peculiar self-assembly ability, likely responsible for the therapeutic effect in animal models of systemic and mucosal candidiasis. The present study analyzed the biological and structural properties of peptides derived from KP by substitution or deletion of the first residue, leaving unchanged the remaining amino acids. The investigated peptides proved to exert differential in vitro and/or in vivo anti-Candida activity without showing toxic effects on mammalian cells. The change of the first residue in KP amino acidic sequence affected the conformation of the resulting peptides in solution, as assessed by circular dichroism spectroscopy. KP-derivatives, except one, were able to induce apoptosis in yeast cells, like KP itself. ROS production and changes in mitochondrial transmembrane potential were also observed. Confocal and transmission electron microscopy studies allowed to establish that selected peptides could penetrate within C. albicans cells and cause gross morphological alterations. Overall, the physical and chemical properties of the first residue were found to be important for peptide conformation, candidacidal activity and possible mechanism of action. Small antimicrobial peptides could be exploited for the development of a new generation of antifungal drugs, given their relative low cost and ease of production as well as the possibility of devising novel delivery systems. [ABSTRACT FROM AUTHOR]

Aflatoxins (AFs) are toxic, carcinogenic, immunosuppressive secondary metabolites produced by some Aspergillus species which colonize crops, including many dietary staple foods and feed components. AFB1 is the prevalent and most toxic among AFs. In the liver, it is biotransformed into AFM1, which is then excreted into the milk of lactating mammals, including dairy animals. AFM1 has been shown to be cause of both acute and chronic toxicoses. The presence of AFM1 in milk and dairy products represents a worldwide concern since even small amounts of this metabolite may be of importance as long-term exposure is concerned. Contamination of milk may be mitigated either directly, decreasing the AFM1 content in contaminated milk, or indirectly, decreasing AFB1 contamination in the feed of dairy animals. Current strategies for AFM1 mitigation include good agricultural practices in pre-harvest and post-harvest management of feed crops (including storage) and physical or chemical decontamination of feed and milk. However, no single strategy offers a complete solution to the issue. [ABSTRACT FROM AUTHOR]

The synthetic peptide T11F (TCRVDHRGLTF), with sequence identical to a fragment of the constant region of human IgM, and most of its alanine-substituted derivatives proved to possess a significant candidacidal activity in vitro. In this study, the therapeutic efficacy of T11F, D5A, the derivative most active in vitro, and F11A, characterized by a different conformation, was investigated in Galleria mellonella larvae infected with Candida albicans. A single injection of F11A and D5A derivatives, in contrast with T11F, led to a significant increase in survival of larvae injected with a lethal inoculum of C. albicans cells, in comparison with infected animals treated with saline. Peptide modulation of host immunity upon C. albicans infection was determined by hemocyte analysis and larval histology, highlighting a different immune stimulation by the studied peptides. F11A, particularly, was the most active in eliciting nodule formation, melanization and fat body activation, leading to a better control of yeast infection. Overall, the obtained data suggest a double role for F11A, able to simultaneously target the fungus and the host immune system, resulting in a more efficient pathogen clearance. [ABSTRACT FROM AUTHOR]

Possible implications and applications of the yeast killer phenomenon in the fight against infectious diseases are reviewed, with particular reference to some wide-spectrum killer toxins (KTs) produced by Wickerhamomyces anomalus and other related species. A perspective on the applications of these KTs in the medical field is provided considering (1) a direct use of killer strains, in particular in the symbiotic control of arthropod-borne diseases; (2) a direct use of KTs as experimental therapeutic agents; (3) the production, through the idiotypic network, of immunological derivatives of KTs and their use as potential anti-infective therapeutics. Studies on immunological derivatives of KTs in the context of vaccine development are also described. [ABSTRACT FROM AUTHOR]

Mycoses still represent relevant opportunistic infections worldwide, although overshadowed in recent years by other severe and more widespread infections. Moreover, deep-seated mycoses are often accompanied by unacceptably high mortality rates. Etiologic agents include endogenous components of the mycobiota, Candida and Malassezia species above all, and exogenous species, both yeasts and filamentous fungi. Old and new fungal pathogens are increasingly characterized by resistance to the existing antifungal agents, making imperative the search for effective and safe new therapeutics. Among the candidate molecules proposed in recent decades, synthetic peptides derived from the complementarity determining and constant regions of diverse antibodies (Abs), as well as the translated products of Ab-encoding genes, have proved of considerable interest. Their anti-infective activities, regardless of the specificity and isotype of the originating Ab, will be briefly presented and discussed in the light of their different mechanisms of action. Intriguing suggestions on the possible function of Abs after their half-life will be presented, following the recent detection, in human serum, of an antimicrobial Ab-derived peptide. Overall, Abs could represent a source of biologically active, highly flexible peptides, devoid of detectable toxicity, which can be easily synthesized and manipulated to be used, alone or in association with already available drugs, for new anti-infective strategies. [ABSTRACT FROM AUTHOR]

The growing problem of antimicrobial resistance highlights the need for alternative strategies to combat infections. From this perspective, there is a considerable interest in natural molecules obtained from different sources, which are shown to be active against microorganisms, either alone or in association with conventional drugs. In this paper, peptides with the same sequence of fragments, found in human serum, derived from physiological proteins, were evaluated for their antifungal activity. A 13-residue peptide, representing the 597–609 fragment within the albumin C-terminus, was proved to exert a fungicidal activity in vitro against pathogenic yeasts and a therapeutic effect in vivo in the experimental model of candidal infection in Galleria mellonella. Studies by confocal microscopy and transmission and scanning electron microscopy demonstrated that the peptide penetrates and accumulates in Candida albicans cells, causing gross morphological alterations in cellular structure. These findings add albumin to the group of proteins, which already includes hemoglobin and antibodies, that could give rise to cryptic antimicrobial fragments, and could suggest their role in anti-infective homeostasis. The study of bioactive fragments from serum proteins could open interesting perspectives for the development of new antimicrobial molecules derived by natural sources. [ABSTRACT FROM AUTHOR]

The synthetic peptide T11F (TCRVDHRGLTF), derived from the constant region of human IgM antibodies, proved to exert a significant activity in vitro against yeast strains, including multidrug resistant isolates. Alanine substitution of positively charged residues led to a decrease in candidacidal activity. A more dramatic reduction in activity resulted from cysteine replacement. Here, we investigated the conformational properties of T11F and its alanine-substituted derivatives by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. Peptide interaction with Candida albicans cells was studied by confocal and scanning electron microscopy. T11F and most of its derivatives exhibited CD spectra with a negative band around 200 nm and a weaker positive band around 218 nm suggesting, together with NMR coupling constants, the presence of a polyproline II (PPII) helix, a conformational motif involved in a number of biological functions. Analysis of CD spectra revealed a critical role for phenylalanine in preserving the PPII helix. In fact, only the F11A derivative presented a random coil conformation. Interestingly, the loss of secondary structure influenced the rate of killing, which turned out to be significantly reduced. Overall, the obtained results suggest that the PPII conformation contributes in characterising the cell penetrating and fungicidal properties of the investigated peptides. [ABSTRACT FROM AUTHOR]